In the normal brewing process there are a number of different liquid residues or effluents resulting from the various operations in the overall process. The liquid residues generally contain a small proportion of dissolved solids, and a small amount of suspended solids, primarily filter aid materials, as well as dissolved carbon dioxide.
In the past, the practice has merely been to discard the liquid residue, but due to pollution considerations, the recent practice has been to treat the liquid residue and remove protenaceous constituents. In the removal treatment, the liquid is initially filtered to remove the suspended solids, and the filtrate is then evaporated. Due to the high concentration of protenaceous material, the concentrated filtrates can be used as a livestock feed. The solids removed by filtration are normally transported to a landfill site and discarded.
When using vacuum filtration equipment to filter the liquid residue or effluent, tremendous quantities of foam are generated due to the dissolved carbon dioxide. It has been found that because of the reduction of pressure during filtration, the carbon dioxide comes out of solution and carbon dioxide bubbles are adsorbed on the filter aid particles or other suspended foreign particles. The carbon dioxide bubbles continue to grow during the filtering operation and cannot be displaced, with the result that the porosity and permeability of the filter are substantially reduced, thereby substantially reducing the rate of filtration.
As a result of the dissolved carbon dioxide, a problem is also encountered in subsequent evaporation of the filtrate. During evaporation the carbon dioxide will come out of solution so that a substantial head of foam is generated in the evaporation vessel. If the foam generation is not controlled, the foam can overflow the vessel or back up into the other equipment.